The present invention relates to a novel process for preparing a reflexible pigment consisting of a metal deposition layer and a resinous coating layer on at least one side thereof and having a length and width of 0.1 to 500 .mu., a thickness of 0.1 to 4 .mu. and a true specific gravity of 1 to 2. The coating composition including the pigment has improved properties such as beautifulness, reflection property, application property, weather-proofing and abrasion property.
Hitherto there has been employed a metal powder such as aluminum powder and bronze powder as a metal pigment for coating composition capable of providing a coated film having metallic luster.
Such a metal powder is prepared by crushing up metal piece into powder. The obtained metal powder has over 30 .mu. in diameter and is poor in flatness. Therefore, a coated surface of coating composition including the metal powder is poor in reflection property, and a beautiful coated surface with a metallic luster is hardly obtained. Also the metal powder may not be completely embedded in coating layer, and the resultant surface is not only poor in abrasion resistance but also rough, and is subjected to oxidation to result in discoloration of surface. Besides the metal powder has poor compatibility with binders used in coating composition and can not be employed for various coating compositions, for instance, in case the metal powder is added to the coating composition including cellulose derivative, the dispersed metal powder deposits out of the coating composition on storage. It is also known that, in case of crushing up a metal piece into the metal powder, stearic acid is added in order to prevent the aggregation of metal powder caused by action of compression, defacement, impingement or shearing in the course of crushing and to give a metallic luster on the resultant metal powder and therefore the obtained metal powder is coated with stearic acid. The layer obtained by employing the metal powder coated with stearic acid, however, has poor abrasion resistance since the affinity between such a metal powder and binder is very small and the powder is difficult to be fixed on the coated surface.
Besides conventional metal powder has a shape of particle or the similar, in other words, is not plane. Thus the coated layer including conventional metal powder has poor hiding ability and therefore large amounts of metal powder are required to give a sufficient metallic luster, which is a disadvantage economically.
The coating composition including conventional metal powder provides a layer having dark gold or silver surface which possesses poor reflexible property. In case of employing colorant as is red, blue or green, such a coating composition can not give a desired beautiful surface having a good metallic luster since it is difficult to provide a clear coating layer.
On the other hand, there has been known a process for preparing a reflexible pigment which is characterized by providing a solvent-soluble releasing layer on a base film, providing thereon a metal leaf which consists of a metal film surfaced on both sides with a solvent-insoluble resinous layer, removing the metal leaf from the base film by dissolving away the releasing layer with organic solvent to give a slurry of the metal leaf in the solvent, and agitating the slurry to crush up the metal leaf into minute pieces (see U.S. Pat. No. 3,692,731 and U.S. Pat. No. 3,697,070).
In the process, a reflexible pigment is obtained as a slurry in solvent, namely, in a wet state. However, the pigment in a wet state can not be sieved to classify into fractions having constant particle sizes. Furthermore, the pigment in a wet state is disadvantageous for its utilization, storage or transportation. Then, it may be reminded to obtain a pigment in a dry state from such a wet pigment. However, for this, there must be employed a tedious separation method such as filtration including the removing of dissolved releasing layer by washing away.
As described above, the process directed to removing a metal leaf from a base film by dissolving away a solvent-soluble releasing layer interposed between the base film and the metal leaf with a solvent is not preferable for the mass-production of a reflexible pigment.